The present invention relates in general to pressurized containers, commonly referred to as aerosol cans, and, more particularly, to methods and apparatus for forming domed aerosol can ends from thin sheet material.
Ends for closing aerosol cans are well known in the art and are normally made of steel and formed with domes which, for aerosol can bottoms, project inwardly into the cans to withstand the internal pressures necessary for properly dispensing materials packaged within the cans. Conventionally, aerosol can ends are made by blanking a workpiece from a sheet of steel, drawing the workpiece to generate a shallow cup with a crown, and then forming a dome into the cup with an upper dome punch and surrounding redraw sleeve which extend into a lower dome die.
While the conventional forming techniques produce satisfactory aerosol can ends when used on conventional thickness sheet steel, such as single reduced steel, the known techniques often result in radial wrinkles in outer peripheral portions of the domes when used with thinner sheet steel, such as double reduced steel. These wrinkles are not only unsightly but also can result in failures of aerosol cans closed with such ends. Due to these failings, the known techniques have thwarted the canning industry""s pursuit of the use of thinner and thinner stock material with regard to making aerosol can ends.
There is, thus, a need for improved methods and apparatus for forming aerosol can ends from thin sheet materials, such as double reduced steel, which overcome the problems currently being encountered in the art. Preferably, the improved methods and apparatus would employ a single acting press having a fixed base and a movable upper punch assembly.
This need is met by the methods and apparatus of the present invention wherein a dome of a domed aerosol can end is initially formed and then a crown of the can end is formed. In this way, material flow within a workpiece from which the can end is formed is controlled to substantially eliminate wrinkling problems associated with the use of sheet material which is thinner than conventionally used, for example double reduced steel. In particular, the peripheral portion of the workpiece is initially clamped between a blank punch and a draw pad, and also between a knockout and a crown ring. An outer first portion of the dome is then formed by an outer redraw sleeve and a dome form die. An inner second portion of the dome is next formed by a dome punch and the dome form die. There may be limited contact of the dome punch with the workpiece during formation of the first portion of the dome and the workpiece may also be clamped between the outer redraw sleeve and the dome form die during formation of the second dome portion. Controlled clamping between the blank punch and the draw pad, between the knockout and the crown ring and between the outer redraw sleeve and the dome form die control material flow for improved formation of the domed aerosol can end with effective elimination of radial wrinkles associated with prior art forming methods and apparatus.
In accordance with one aspect of the present invention, a method for forming a domed aerosol can end from a sheet of material in a press having a fixed base and a movable punch assembly comprises blanking a workpiece from the sheet of material and holding the workpiece between a blank punch carried by the punch assembly and a draw pad carried by the base. The workpiece is also held between a knockout carried by the punch assembly and a crown ring carried by the base. The blank punch is advanced to form an outer crown lip around the periphery of the workpiece and an outer redraw sleeve carried by the punch assembly is advanced, to form an outer portion of a dome of the domed aerosol can end between the redraw sleeve and a dome form die on the base. The knockout and the crown ring hold the workpiece to control the flow of material into the outer portion of the dome. A dome punch is advanced to form an inner portion of the dome with the dome form die, the knockout and the crown ring holding the workpiece to control the flow of material into the inner portion of the dome. The outer crown lip is shortened in accordance with the flow of material. Finally, the dome form die collapses to form a crown for the domed aerosol can end.
The method for forming a domed aerosol can end may further comprise holding the outer portion of the dome between the redraw sleeve and the dome form die to control the flow of material into the inner portion of the dome as the dome punch advances to form the inner portion of the dome. The steps of advancing an outer redraw sleeve and advancing a dome punch may be performed to substantially completely form the outer portion of the dome before the dome punch contacts the workpiece.
In accordance with another aspect of the present invention, a method of forming a domed aerosol can end from a sheet of material in a press having a fixed base and a movable punch assembly comprises initially forming a dome of the domed aerosol can end, and then forming a crown of the domed aerosol can end. The step of forming a dome of the domed aerosol can end may comprise blanking a workpiece from the sheet of material, holding the workpiece between a blank punch carried by the punch assembly and a draw pad carried by the base and holding the workpiece between a knockout carried by the punch assembly and a crown ring carried by the base. The blank punch and draw pad are advanced to form an outer crown lip around the periphery of the workpiece. An outer redraw sleeve and a dome punch, both carried by the punch assembly, are advanced to form an outer portion of the dome of the domed aerosol can end between the outer redraw sleeve and a dome form die. The dome punch is further advanced to form an inner portion of the dome with the dome form die, the knockout and the crown ring holding the workpiece to control the flow of material into the inner portion of the dome and the outer crown lip shortening in accordance with the flow of material.
The method of forming a domed aerosol can end may further comprise forming a crown of the domed aerosol can end by collapsing the dome form die. The step of forming a dome of the domed aerosol can end may further comprise holding the outer portion of the dome between the outer redraw sleeve and the dome form die to control the flow of material into the inner portion of the dome as the dome punch advances to form the inner portion of the dome.
In accordance with yet another aspect of the present invention, a method for forming a dome of a domed aerosol can end from a workpiece blanked from a sheet of material in a press having a fixed base and a movable punch assembly comprises holding the workpiece between a knockout carried by the punch assembly and a crown ring carried by the base and advancing an outer redraw sleeve and a dome punch, both carried by the punch assembly, to form an outer portion of the dome of the domed aerosol can end between the outer redraw sleeve and a dome form die. The dome punch is further advanced to form an inner portion of the dome with the dome form die, the knockout and the crown ring holding the workpiece to control the flow of material into the inner portion of the dome. The method for forming a dome of a domed aerosol can end may further comprise the step of holding the outer portion of the dome between the outer redraw sleeve and the dome form die to control the flow of material into the inner portion of the dome as the dome punch advances to form the inner portion of the dome.
In accordance with still another aspect of the present invention, apparatus for forming a domed aerosol can end from a sheet of material in a press having a fixed base and a movable punch assembly comprises a blank punch carried by the punch assembly and a crown ring carried by the base, the crown ring being opposite the blank punch for holding a workpiece during formation of the domed aerosol can end. An outer redraw sleeve and a dome punch are carried by the punch assembly with a dome form die mounted on the base. The outer redraw sleeve forms an outer first portion of a dome for the domed aerosol can end with the dome form die prior to the dome punch forming a second inner portion of the dome with the dome form die. In the apparatus for forming a domed aerosol can end the outer redraw sleeve together with the dome form die may hold the workpiece as the dome punch forms the second portion of the dome of the domed aerosol can end. The apparatus may further comprise means for collapsing the dome form die after the dome is formed to form a crown of the domed aerosol can end.
In accordance with an additional aspect of the present invention, apparatus for forming a domed aerosol can end from a sheet of material in a press having a fixed base and a movable punch assembly comprises a blank punch carried by the punch assembly and a crown ring carried by the base, the crown ring being opposite the blank punch for holding a workpiece during formation of the domed aerosol can end. An outer redraw sleeve and a dome punch are carried by the punch assembly while a dome form die is mounted on the base. The outer redraw sleeve forms an outer first portion of a dome for the domed aerosol can end with the dome form die and, together with the dome form die, holds the workpiece as an inner second portion of the dome is formed by the dome punch with the dome form die.
The invention of the present application will be better understood from a review of the following detailed description, the accompanying drawings which form part of the specification and the appended claims.